For example, in a semiconductor manufacturing apparatus to which various kinds of gas used for manufacturing a semiconductor are supplied, a mass flow controller is provided for each gas supply channel to adjust the flow rate of the gas. Conventionally, a pressure regulator is connected in series to each mass flow controller for preventing an extreme change in pressure in the channel to which the mass flow controller is attached, thereby facilitating flow rate control.
A basic flow rate control method for the mass flow controller is the PID control. For example, there has been known a feed back control based on a variation of the PID control disclosed in the patent document 1. Specifically, according to the method disclosed in the patent document 1, the feed back control value is calculated by performing a PID calculation on the deviation and multiplying the calculation result by a function whose value increases as the flow rate setting value decreases.
Recently, a system configuration has become popular in which a regulator is provided only for a fluid supply source, such as a cylinder, rather than for each supply channel, although the mass flow controller is provided for each supply channel divaricated from the fluid supply source.
However, for example, this system configuration has the following disadvantage. That is, if one of the supply channels is suddenly closed, or the flow rate of one of the mass flow controllers is largely changed, the resulting pressure change affects the other supply channel or mass flow controllers (this is referred to as a crosstalk). As a result, the conventional control method based on the assumption that the pressure regulator controls the pressure change to some extent cannot achieve adequate flow rate control.
More specifically, in the case where the control method disclosed in the patent document 1 is used, if the pressure on the primary side (the pressure on the upstream side of the mass flow controller (a flow rate sensor section) changes beyond a certain level, the flow rate excessively responds to the change of the pressure and changes beyond a prescribed level.
Such a problem of flow rate change due to the pressure change is caused not only by the crosstalk but also by other factors. In addition, such a problem occurs not only when the pressure on the primary side changes but also when the pressure on the secondary side changes.
However, under the current circumstance in which higher speed and precision are needed in the control of the raw material gas or the like used in semiconductor processes, the speed of following the change of the flow rate setting value (the speed of response) cannot be sacrificed to suppress the excessive response described above.    Patent Document 1 Japanese Patent Laid-Open No. 2004-280689